diff --git a/compiler/global/clocks.ml b/compiler/global/clocks.ml
index 8bb2f4b..2094e3c 100644
--- a/compiler/global/clocks.ml
+++ b/compiler/global/clocks.ml
@@ -99,6 +99,19 @@ and unify_list t1_list t2_list =
   try List.iter2 unify t1_list t2_list
   with _ -> raise Unify
 
+let rec skeleton ck = function
+  | Tprod ty_list ->
+      (match ty_list with
+        | [x] -> Ck ck
+        | l -> Cprod (List.map (skeleton ck) l))
+  | Tarray _ | Tid _ | Tinvalid -> Ck ck
+
+let unprod ct =
+  let rec f acc ct = match ct with
+    | Ck ck -> ck::acc
+    | Cprod ct_l -> List.fold_left f acc ct_l
+  in
+  f [] ct
 
 let prod ck_l = match ck_l with
   | [ck] -> Ck ck
@@ -108,6 +121,10 @@ let rec root_ck_of ck = match ck_repr ck with
   | Cbase | Cvar _ -> ck
   | Con(ck,_,_) -> root_ck_of ck
 
+let rec last_clock ct = match ct with
+  | Ck ck -> ck
+  | Cprod l -> last_clock (Misc.last_element l)
+
 (*
 let rec tuple ck = function
   | Tprod ty_list ->
diff --git a/compiler/global/signature.ml b/compiler/global/signature.ml
index c31c0d5..12eb04d 100644
--- a/compiler/global/signature.ml
+++ b/compiler/global/signature.ml
@@ -59,11 +59,10 @@ type const_def = { c_type : ty; c_value : static_exp }
 (** { 3 Signature helper functions } *)
 
 type error =
-  | Eckvar_unbound of name option * name
   | Eckvar_unbound_input of name option * name
   | Eckvar_unbound_ouput of name option * name
 
-exception SignatureError of error
+exception SignatureError of name option * name
 
 let message loc e = begin match e with
   | Eckvar_unbound_input(var_name,ck_name) ->
@@ -76,8 +75,6 @@ let message loc e = begin match e with
       Format.eprintf "%a%s sampled ouput%s should be returned with its sampling value %s.@."
         print_location loc
         a name ck_name
-  | Eckvar_unbound(var_name,ck_name) ->
-      Format.eprintf "%aThe variable %s is unbound.@." print_location loc ck_name
   end;
   raise Errors.Error
 
@@ -98,7 +95,7 @@ let check_signature s =
       | Cbase -> ()
       | Con(ck,_,x) ->
           if not (NamesSet.mem x env)
-          then raise (SignatureError (Eckvar_unbound (n,x)));
+          then raise (SignatureError (n,x));
           f ck
     in
     f arg.a_clock
@@ -106,11 +103,11 @@ let check_signature s =
   (*initial env with only the inputs*)
   let env = append NamesSet.empty s.node_inputs in
   (try List.iter (check env) s.node_inputs
-  with SignatureError (Eckvar_unbound (x,c)) ->
+  with SignatureError (x,c) ->
     message s.node_loc (Eckvar_unbound_input (x,c)));
   let env = append env s.node_outputs in
   try List.iter (check env) s.node_outputs
-  with SignatureError (Eckvar_unbound (x,c)) ->
+  with SignatureError (x,c) ->
     message s.node_loc (Eckvar_unbound_ouput (x,c))
 
 
diff --git a/compiler/main/hept2mls.ml b/compiler/main/hept2mls.ml
index c9bc74a..a54402b 100644
--- a/compiler/main/hept2mls.ml
+++ b/compiler/main/hept2mls.ml
@@ -98,15 +98,15 @@ let rec translate_extvalue e =
           mk_extvalue (Wfield (translate_extvalue e, fn))
     | _ -> Error.message e.Heptagon.e_loc Error.Enormalization
 
-let translate ({ Heptagon.e_desc = desc; Heptagon.e_ty = ty; Heptagon.e_level_ck = b_ck;
+let rec translate ({ Heptagon.e_desc = desc; Heptagon.e_ty = ty; Heptagon.e_level_ck = b_ck;
                  Heptagon.e_ct_annot = a_ct; Heptagon.e_loc = loc } as e) =
   let desc = match desc with
     | Heptagon.Econst _
     | Heptagon.Evar _
-    | Heptagon.Ewhen _
     | Heptagon.Eapp({ Heptagon.a_op = Heptagon.Efield }, _, _) ->
         let w = translate_extvalue e in
         Eextvalue w
+    | Heptagon.Ewhen (e,c,x) -> Ewhen (translate e, c, x)
     | Heptagon.Epre(None, e) ->
         Efby(None, translate_extvalue e)
     | Heptagon.Epre(Some c, e) ->
diff --git a/compiler/main/mls2obc.ml b/compiler/main/mls2obc.ml
index 83e09c6..993352d 100644
--- a/compiler/main/mls2obc.ml
+++ b/compiler/main/mls2obc.ml
@@ -209,6 +209,9 @@ let rec translate map e =
         let e = translate_extvalue map (assert_1 e_list) in
         let idx_list = List.map (fun idx -> mk_exp tint (Econst idx)) idx in
           Epattern (pattern_of_idx_list (pattern_of_exp e) idx_list)
+    | Minils.Ewhen(e,_,_) ->
+        let e = translate map e in
+        e.e_desc
   (* Already treated cases when translating the [eq] *)
     | Minils.Eiterator _ | Minils.Emerge _ | Minils.Efby _
     | Minils.Eapp ({Minils.a_op=(Minils.Enode _|Minils.Efun _|Minils.Econcat
@@ -231,6 +234,7 @@ and translate_act map pat
     ({ Minils.e_desc = desc } as act) =
     match pat, desc with
    (* When Merge *)
+    | pat, Minils.Ewhen (e,_,_) -> translate_act map pat e
     | Minils.Evarpat x, Minils.Emerge (y, c_act_list) ->
         let x = var_from_name map x in
         let translate_c_extvalue (c, w) =
diff --git a/compiler/minils/analysis/clocking.ml b/compiler/minils/analysis/clocking.ml
index 5d5c2b2..4b671ce 100644
--- a/compiler/minils/analysis/clocking.ml
+++ b/compiler/minils/analysis/clocking.ml
@@ -97,7 +97,7 @@ let typing_app h base pat op w_list = match op with
       in
       let env_pat = build_env node.node_outputs pat_id_list [] in
       let env_args = build_env node.node_inputs w_list [] in
-      (* implement with Cbase as base, replace name dep by ident dep *)
+(* implement with Cbase as base, replace name dep by ident dep *)
       let rec sigck_to_ck sck = match sck with
         | Signature.Cbase -> base
         | Signature.Con (sck,c,x) ->
@@ -118,55 +118,89 @@ let typing_app h base pat op w_list = match op with
       Clocks.prod (List.map (fun a -> sigck_to_ck a.a_clock) node.node_outputs)
 
 
-let typing_eq h { eq_lhs = pat; eq_rhs = e } =
-  (* typing the expression *)
-  let ct,base = match e.e_desc with
-    | Eextvalue w
-    | Efby (_, w) ->
-        let ck = typing_extvalue h w in
-        Ck ck, ck
-    | Emerge (x, c_e_list) ->
-        let ck = ck_of_name h x in
-        List.iter (fun (c,e) -> expect_extvalue h (Con (ck,c,x)) e) c_e_list;
-        Ck ck, ck
-    | Estruct l ->
-        let ck = fresh_clock () in
-        List.iter (fun (_, e) -> expect_extvalue h ck e) l;
-        Ck ck, ck
-    | Eapp({a_op = op}, args, r) ->
-        let ck_r = match r with
-          | None -> fresh_clock ()
-          | Some(reset) -> ck_of_name h reset in
-        let ct = typing_app h ck_r pat op args in
-        ct, ck_r
-    | Eiterator (_, _, _, pargs, args, r) ->        (*TODO*)
-        (* Typed exactly as a fun or a node... *)
-        let ck_r = match r with
-          | None -> fresh_clock()
-          | Some(reset) -> ck_of_name h reset
-        in
-        List.iter (expect_extvalue h ck_r) pargs;
-        List.iter (expect_extvalue h ck_r) args;
-        Ck ck_r, ck_r
-  in
-  e.e_base_ck <- base;
-  begin
-    try unify ct e.e_ct
-    with Unify ->
-      eprintf "Incoherent clock annotation.@\n";
-      error_message e.e_loc (Etypeclash (ct,e.e_ct))
-  end;
-  e.e_ct <- ct;
- (* typing the full equation *)
-  let pat_ct = typing_pat h pat in
-  begin
-    try unify ct pat_ct
-    with Unify ->
-      eprintf "Incoherent clock between right and left side of the equation@\n";
-      error_message e.e_loc (Etypeclash (ct, pat_ct))
-  end
 
 
+let typing_eq h { eq_lhs = pat; eq_rhs = e } =
+  (* typing the expression, returns ct, ck_base *)
+  let rec typing e =
+    let ct,base = match e.e_desc with
+      | Eextvalue w
+      | Efby (_, w) ->
+          let ck = typing_extvalue h w in
+          Ck ck, ck
+      | Ewhen (e,c,n) ->
+          let ck_n = ck_of_name h n in
+          let base = expect (skeleton ck_n e.e_ty) e in
+          skeleton (Con (ck_n, c, n)) e.e_ty, base
+      | Emerge (x, c_e_list) ->
+          let ck = ck_of_name h x in
+          List.iter (fun (c,e) -> expect_extvalue h (Con (ck,c,x)) e) c_e_list;
+          Ck ck, ck
+      | Estruct l ->
+          let ck = fresh_clock () in
+          List.iter (fun (_, e) -> expect_extvalue h ck e) l;
+          Ck ck, ck
+      | Eapp({a_op = op}, args, r) ->
+          (* base clock of the node *)
+          let ck_r = match r with
+            | None -> fresh_clock ()
+            | Some(reset) -> ck_of_name h reset in
+          let ct = typing_app h ck_r pat op args in
+          ct, ck_r
+      | Eiterator (it, {a_op = op}, _, pargs, args, r) ->
+          (* base clock of the node *)
+          let ck_r = match r with
+            | None -> fresh_clock()
+            | Some(reset) -> ck_of_name h reset
+          in
+          let ct = match it with
+            | Imap -> (* exactly as if clocking the node *)
+                typing_app h ck_r pat op args
+            | Imapi -> (* clocking the node with the extra [i] input on [ck_r] *)
+                let i (* stubs [i] as 0 *) =
+                  mk_extvalue ~ty:Initial.tint ~clock:ck_r (Wconst (Initial.mk_static_int 0))
+                in
+                typing_app h ck_r pat op (args@[i])
+            | Ifold | Imapfold ->
+                (* clocking node with equality constaint on last input and last output *)
+                let ct = typing_app h ck_r pat op args in
+                unify_ck (Clocks.last_clock ct) (Misc.last_element args).w_ck;
+                ct
+            | Ifoldi -> (* clocking the node with the extra [i] and last in/out constraints *)
+                let i (* stubs [i] as 0 *) =
+                  mk_extvalue ~ty:Initial.tint ~clock:ck_r (Wconst (Initial.mk_static_int 0))
+                in
+                let rec insert_i args = match args with
+                  | [] -> [i]
+                  | [l] -> i::[l]
+                  | h::l -> h::(insert_i l)
+                in
+                let ct = typing_app h ck_r pat op (insert_i args) in
+                unify_ck (Clocks.last_clock ct) (Misc.last_element args).w_ck;
+                ct
+          in
+          ct, ck_r
+    in
+    e.e_base_ck <- base;
+    (try unify ct e.e_ct
+     with Unify ->
+       eprintf "Incoherent clock annotation.@\n";
+       error_message e.e_loc (Etypeclash (ct,e.e_ct)));
+    e.e_ct <- ct;
+    ct, base
+  and expect expected_ct e =
+    let actual_ct,base = typing e in
+    (try unify actual_ct expected_ct
+     with Unify -> error_message e.e_loc (Etypeclash (actual_ct, expected_ct)));
+    base
+  in
+  let ct,base = typing e in
+  let pat_ct = typing_pat h pat in
+  (try unify ct pat_ct
+    with Unify ->
+      eprintf "Incoherent clock between right and left side of the equation.@\n";
+      error_message e.e_loc (Etypeclash (ct, pat_ct)))
+
 let typing_eqs h eq_list = List.iter (typing_eq h) eq_list
 
 let append_env h vds =
diff --git a/compiler/minils/minils.ml b/compiler/minils/minils.ml
index eefcb9a..4aae37d 100644
--- a/compiler/minils/minils.ml
+++ b/compiler/minils/minils.ml
@@ -53,7 +53,7 @@ and extvalue_desc =
 
 and exp = {
   e_desc            : edesc;
-  e_level_ck        : ck; (* when no data dep, execute the exp on this clock (set by [switch] *)
+  e_level_ck        : ck; (*when no data dep, execute the exp on this clock (set by [switch] *)
   mutable e_base_ck : ck;
   mutable e_ct      : ct;
   e_ty              : ty;
@@ -65,13 +65,14 @@ and edesc =
                        (** static_exp fby extvalue *)
   | Eapp of app * extvalue list * var_ident option
                        (** app ~args=(extvalue,extvalue...) reset ~r=ident *)
+  | Ewhen of exp * constructor_name * var_ident  (** e when C(c) *)
   | Emerge of var_ident * (constructor_name * extvalue) list
                        (** merge ident (Constructor -> extvalue)+ *)
   | Estruct of (field_name * extvalue) list
                        (** { field=extvalue; ... } *)
   | Eiterator of iterator_type * app * static_exp
                  * extvalue list * extvalue list * var_ident option
-                       (** map f <<n>> (extvalue, extvalue...) reset ident *)
+                       (** map f <<n>> <(extvalue)> (extvalue) reset ident *)
 
 and app = { a_op: op; a_params: static_exp list; a_unsafe: bool }
     (** Unsafe applications could have side effects
diff --git a/compiler/minils/mls_mapfold.ml b/compiler/minils/mls_mapfold.ml
index 0cb5d02..ff66125 100644
--- a/compiler/minils/mls_mapfold.ml
+++ b/compiler/minils/mls_mapfold.ml
@@ -85,6 +85,9 @@ and edesc funs acc ed = match ed with
           (c,w), acc in
       let c_w_list, acc = mapfold aux acc c_w_list in
         Emerge(x, c_w_list), acc
+  | Ewhen(e,c,x) ->
+      let e, acc = exp_it funs acc e in
+      Ewhen(e,c,x), acc
   | Estruct n_w_list ->
       let aux acc (n,w) =
         let w, acc = extvalue_it funs acc w in
diff --git a/compiler/minils/mls_printer.ml b/compiler/minils/mls_printer.ml
index 10b00f3..138e3de 100644
--- a/compiler/minils/mls_printer.ml
+++ b/compiler/minils/mls_printer.ml
@@ -102,6 +102,8 @@ and print_exp_desc ff = function
       fprintf ff "@[<2>%a@,%a@]" print_app (app, args) print_every reset
   | Emerge (x, tag_w_list) ->
       fprintf ff "@[<2>merge %a@ %a@]" print_ident x print_tag_w_list tag_w_list
+  | Ewhen (e,c,x) ->
+      fprintf ff "@[<2>(%a@ when %a(%a))@]" print_exp e print_qualname c print_ident x
   | Estruct f_w_list ->
       print_record (print_couple print_qualname print_extvalue """ = """) ff f_w_list
   | Eiterator (it, f, param, pargs, args, reset) ->
diff --git a/compiler/minils/mls_utils.ml b/compiler/minils/mls_utils.ml
index ed55270..0b62477 100644
--- a/compiler/minils/mls_utils.ml
+++ b/compiler/minils/mls_utils.ml
@@ -193,10 +193,9 @@ let eq_find id = List.find (fun eq -> List.mem id (Vars.def [] eq))
 let ident_list_of_pat pat =
   let rec f acc pat = match pat with
     | Evarpat id -> id::acc
-    | Etuplepat [] -> acc
-    | Etuplepat (pat::pat_l) -> f (f acc pat) (Etuplepat pat_l)
+    | Etuplepat pat_l -> List.fold_left f acc pat_l
   in
-  f [] pat
+  List.rev (f [] pat)
 
 
 let args_of_var_decs =